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Discussion Starter · #1 · (Edited)
I would have thought that this was a well settled issue but a recent conversation on this forum proved to me that it's another one of those never ending misconceptions.

So why would this be of importance to a shooter? All shooters have an idea of what they believe is the kind of performance that they think will serve their needs best and if your rifle isn't performing to that standard then you need to troubleshoot the system to find out why. Some people want minute-of-man groups and others want bug holes, no matter which kind of shooter you are you need to create a way to identify where you can improve the system so that you get the performance you are looking for and knowing these terms will do that for you.

Since no discussion about weapon system performance can be had without the proper understanding of terms I'd like to define and explain the difference between these two terms.

In simplest terms,

Accuracy - the measurement of how close the center of the GROUP comes to the shooter's point of aim (POA).

Precision - the measurement of how close the individual BULLETS come to each other.

From the book "Understanding Firearm Ballistics", 6th Edition, by Robert A. Rinker
  • Accuracy is how close a strike is to where it was intended to hit and measurements are to that one point only.
  • Precision is how well the shots grouped and the measure is to each other no matter how close or far from a target center.
These words mean different things under different circumstances but in our sport these are the words that the ballisticians use to describe the performance of a weapon system, they weren't picked arbitrarily, they were picked because they create very specific, quantifiable data that can be used to MEASURE the performance of a system. These are not words that I choose to use, they are THE terms used as a standard by which the scientists can compare performance results. You can't just use terms that feel good or sound right to you, you have to use the proper terminology, terms that the industry uses so that we can all understand the conversation. More importantly, the words accuracy and precision actually help troubleshoot your groups by creating distinct action/reaction links. One poster felt that the word 'consistent' was a valid term when describing his groups, unfortunately that word is vague and normally is used to describe the appearance of a group of events or the overall system in generalized terms rather than in some quantified, measurable way. You can have consistently bad performance just as you can have consistently good performance, the same word can be used to describe either result. On the other hand, a group is either accurate or it's not, it's precise or it's not, it's both or it's not, these words can't be used to describe both kinds of results.

The Chief Ballistician for Berger Bullets and competition shooter, Bryan Litz in his book "Accuracy and Pricision For Long Range Shooting A Practical Guide for Riflemen" explains that,
Even the basic distinction between accuracy and precision is not well understood by many long range shooters.
He goes on to say,
Of course it's common knowledge that small groups are good (this is precision) and a good zero and trajectory prediction are important (accuracy). But beyond this basic guidance, little is known or discussed about the relative importance of the various elements from a quantitative point of view.
He then explains that in order to improve your hit probability you need to be able to quantify the impact errors and make well informed decisions about how to improve your weapon system. You do that by relating these two terms to specific parts of the system. Mr. Litz then says,
Precision is commonly expressed as group size...Centering the group...is a challenge of accuracy...
So to improve the performance of your weapon system you need to understand how to apply each word and understand which parts of the weapon system are connected to each word.

Since the word accuracy, in the context of a ballistics, compares the group's center to the POA it's easy to understand that it is connected to the zeroing of the rifle. If groups aren't centered on your point of aim then your accuracy is poor. That should make you recognize that anything that can cause a negative impact on the rifle's zero will be suspect. At this point you break down all the possible culprits by using the standard shooting system triad; rifle, ammo, shooter. Ask yourself what could the shooter do to cause poor accuracy (wrong group zero), next ask yourself what kind of ammo problem would effect the zero, and finally what could the rifle do that would cause the zero to be off. In the real world it is most common for the shooter or sighting system to be the cause of accuracy errors. So seeing that your group is not centered on your POA should lead you to look at your shooting technique and the sights first; more often then not one or the other will fix the accuracy problem.

Precision, or the size of the group, is analyzed the same way as above but more often then not you will find that most precision issues are either the stock fit or the ammo (assuming that you have worked out any accuracy problem).

The best way to troubleshoot your group problems is to start analyzing the precision of the group first and then work on the accuracy. First you work on getting the size of group that you believe you need, this is always the longest part of the process because it's hard to decide when enough is enough. The shooter needs to review his shooting technique, the ammo needs to be built to precise standards, and the rifle needs to be assembled as precisely as possible. It may take a long time to fix all the problems you find in each area but you have to temper the effort you make with the reality of the kind of shooting you expect to do. It makes no sense to tune a rifle to sub-MOA groups when you intent to shoot a 36" square target from 25 yards. After your groups have been reduced as much as you think is reasonable then you move on to the accuracy issue, get the group centered on the POA. This can be a problem for some shooters because in many instances it requires us to admit that we are the problem. It can also cause us to pull our hair out because any sighting problem is usually caused by very small errors in fit or alignment of the rifle parts, remember that it only takes a few thousandths of an inch error in the sights to cause one inch of bullet impact error. In the real world this process repeats itself over and over until you get to where you want the system to perform.

Using these terms as a guide to improving your weapon system should help you to quickly resolve any performance problems and provide for long term solutions.
 

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Discussion Starter · #4 ·
As Litz said, even the basic distinction is lost among a lot of shooters. Everybody has their own understanding of things and it works for them but for me knowing these terms and how they apply helps reduce the time it takes to troubleshoot my groups and it allows me to communicate more intelligently with the experts. If some people choose their own version of reality then that's their business but I prefer to understand the language of those who design and build our toys. I'm an old dog but I can still learn new tricks.
 
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